Adolescence is a critical period of neurological, biological, and social growth during the transition from childhood to adulthood. Healthy adolescence is defined by an increasing ability to control impulsive behavior. Deviations from normal development that are produced by substance use and environmental factors are thought to contribute to poor impulse control. Preadolescent problems with impulse control and family histories of substance use disorders appear to increase the risk of earlier substance use initiation during adolescence. It is unknown whether poor impulse control contributes to, or is the result of, substance use and whether poor impulse control and substance use interact across adolescent development to produce increasingly negative outcomes. During a 5-year longitudinal study, we will determine how preadolescent impulse control predicts, and/or later substance use involvement alters, development of adolescent impulse control. We will recruit 360 preadolescent boys and girls (ages 10-12) with and without family histories of substance use disorders, none of whom have initiated regular substance use. Adolescents will complete assessments at study entry and again every 6 months through middle adolescence (from ages 10 through 17), when the risk of developing substance use is heightened. We will monitor changes in substance use involvement, environmental stressors, physical maturation, and impulse control. The project will examine these complex developmental influences on impulse control and substance use involvement by: (1) determining to what extent preadolescent levels of impulse control differ as a function of family history of substance use disorders; (2) determining to what extent preadolescent levels of impulse control predict regular substance use; (3) characterizing impulse control of normal adolescence, and how this development differs with varying levels of substance use; (4) determining how the development of impulse control among substance users is related to the progression of substance use involvement; (5) determining the relative influence of family histories of substance use disorders, substance use involvement, environmental stressors, and maturation on impulse control development across adolescence; (6) determining if there is a reciprocal relationship between impulse control and substance use involvement, such that they have increasingly negative behavioral outcomes that affect each other during adolescence; and (7) testing the relationships of impulse control, family history of substance use disorders, environmental stressors, and substance use involvement within the context of two leading models. By carrying out these aims, we will determine when, how, and to what extent individual differences in these factors contribute to the initiation and progression of substance use; how subsequent substance use affects development of impulse control; and whether our findings support two leading theoretical models of adolescent substance use involvement.